Research is designed to yield new insights into basic mechanisms of heredity in higher organisms. Projects investigate, from several avenues of approach, the nature of cellular structures and processes involved in homologous chromosome pairing, genetic recombination, crossover interference, the maintenance of chiasmate association, and chromosome distribution to gametes. Techniques include cytogenetic engineering, laboratory experimental treatment and cytological observation. The organism selected for study offers a unique combination of excellence of meiotic cytology, an array of available meiotic mutants, morphological chromosome variants and polysomics, a very good genetic map and probability of general applicability of findings.---Specific projects are focused on: (1) search for highly specialized homologue pairing sites within chromosome arms, based on direct cytological observations of complex chromosome rearrangement heterozygotes; (2) tests of the dynamics of establishment of homologue pairing which is effective for crossing over by means of cytological observations of special hyperploid complements of complex rearrangement heterozygotes; (3) definition of the stage or stages of advance forms of homologue interaction in preparation for synapsis utilizing newly developed and refined techniques which will allow more precise observations than have been possible in the past; (4) tests of the nature of the mechanisms of chiasma maintenance and second division dyad integrity maintenance, by use of experimental procedures which allow observation of disruption of these mechanisms, and (5) ultrastructural studies of cells from meiotic mutant material, which may allow dissection of components of meiotic processes for separate observation.---This research is expected to contribute to fundamental understanding of problems of great human concern. Basic knowledge of the mechanism of chromosome pairing and recombination may contribute to understanding of the generation of antibody diversity by the immune system, as well as to understanding of the etiology of malignancy. The nature of the chiasmate association, and its induced disruption has special relevance for understanding and preventing initial steps in the production of Down's syndrome and other human aneuploid abnormalities.